Video signal processing method and device

ABSTRACT

In a video signal processing method of processing a luminance signal of a video signal generated by causing a CCD to receive light transmitted through color filters, a control signal yf 1  is generated by calculating Cy/Y using a complementary color signal Cy and a luminance signal Y, and coring correction is performed to the luminance signal by using the control signal yf 1.  The characteristic difference between the color filters is suppressed, and, as a result, flickers are suppressed from being generated.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a video signal processing methodand a video signal processing device each of which is applied to animage-pickup apparatus (e.g., video camera or the like) and performs apredetermined correction process to a luminance signal of a video signalgenerated by an image pickup operation performed by a solid state imagepickup device.

[0003] 2. Description of Related Art

[0004] Conventionally, in a so-called single-plate color video camerausing only one sold state image pickup device (charge coupled device:CCD), color filters having different spectral characteristics arearranged on the solid state image pickup device in units of pixels, andsignals depending on color components of an object image are obtainedfrom the respective pixels, thereby generating a color video signal. Forthe video signal generated as described above, color components of theobject image are sequentially output according to the arrangement of thecolor filters, and the color signals are multiplexed. Since the soldstate image pickup device can know a specific pixel which a read signalis obtained from, a color signal can be easily separated and demodulatedfrom an output video signal from the solid state image pickup device.

[0005] It is an important factor to increase the sensitivity of thissingle-plate color video camera. Therefore, as color filters employed inthe single-plate color video camera, a complementary color filter havingtransmittance for white light which is higher than that of primary colorfilters such as R (red), G (green), and B (blue) filters are frequentlyused.

[0006] As the complementary color filter, a filter obtained by arrangingMg (magenta), G (green), Cy (cyan), and Ye (yellow) filters or a filterobtained by arranging W (white), G, Cy, and Ye filters is employed.

[0007] In particular, a complementary color filter obtained by arrangingW, G, Cy, and Ye filters shown in FIG. 1 is frequently employed in asolid state image pickup device, which is often used in recent years,using a so-called all-pixel reading system in which signal charges ofall pixels are independently read for a one-field period and outputwithout mixing them so that high horizontal-and vertical resolutions ofan object can be obtained, even if the object is quickly moving.

[0008] When the complementary color filter obtained by arranging the W,G, Cy, and Ye shown in FIG. 1 is arranged in a solid state image pickupdevice which employs the all-pixel reading system as a reading system, aspectral difference may be often generated, as indicated by a hatchedportion in FIG. 2, between a luminance signal (Ya=W+G) consisting of Wand G and indicated by Ya in FIG. 2 and a luminance signal (Yb=Cy+Ye)consisting of Cy and Ye and indicated by Yb in FIG. 2. It is assumedthat the luminance signal Ya is used for a first field and that theluminance signal Yb is used for a second field.

[0009] As described above, assume that a spectral difference isgenerated between the luminance signal Ya consisting of W and G and theluminance signal Yb consisting of Cy and Ye. In this case, thereafter,when the first and second fields are formed by using the luminancesignals Ya and Yb later, and an image is displayed on a display device,flickers are generated on the screen of the display device.

[0010] Since the spectral difference as described above is caused by acharacteristic difference between color filters of a complementary colorfilter arranged on a solid state image pickup device, it is verydifficult (virtually, impossible) to correct the spectral difference bysignal processing performed by a circuit arrangement. Therefore,flickers cannot be suppressed.

[0011] By the way, the basic processing procedure of a color videocamera includes the process of causing a solid state image pickup deviceto detect an image as charges accumulated in a photoelectric conversionelement and the process of causing a low-pass filter to convert adigital signal, obtained by quantizing a quantity of charge, into ananalog image signal.

[0012] Although a substantial resolution is determined by the number ofpixels arranged on a CCD solid state image pickup device, after asampling process and a restoring process, a false signal caused by anessentially high spatial frequency component is inevitably generated.

[0013]FIG. 3 shows an example of a color filter array. Here, a colorfilter array consisting of W (white), G (green), Cy (cyan), and Ye(yellow) is used, and the four pixels are used as a base unit. In FIG.3, reference symbol Px denotes a pixel pitch in the horizontaldirection, and reference symbol Py denotes a pixel pitch in the verticaldirection.

[0014] With respect to the horizontal direction, a luminance resolutioncorresponding a spatial frequency of 1/Px can be expected. However, forexample, due to the difference between the intensities of G and Ye, thefollowing false signal is generated when a carrier frequency isrepresented by fs:

(π/2)×(W−G) sin(2π×fs×t)

SUMMARY OF THE INVENTION

[0015] It is an object of the present invention to provide a videosignal processing method and a video signal processing device each ofwhich can easily suppress flickers based on the characteristicdifference of a complimentary color filter by signal processingperformed by a circuit arrangement.

[0016] It is another object of the present invention to provide aluminance signal processing circuit for a color video camera which canconsiderably suppress a false signal generated by luminance signalprocessing for a color video camera.

[0017] To achieve the object described above, from the first aspect ofthe present invention, there is provided a video signal processingmethod of processing a luminance signal of a video signal generated bycausing a solid state image pickup device to receive light transmittedthrough color filters, comprising the steps of: calculating an outputsignal from a specific pixel of the solid state image pickup device;calculating an average of output signals from all pixels of the solidstate image pickup device; generating a control signal by apredetermined arithmetic operation using the output signal from thespecific pixel and the average of the output signals from all the pixelsof the solid state image pickup device; and performing a predeterminedcorrection process to the luminance signal by using the control signal.

[0018] Further, from the second aspect of the present invention, thereis provided a video signal processing method of processing a luminancesignal of a video signal generated by causing a solid state image pickupdevice to receive light transmitted through color filters, comprisingthe steps of: calculating an output signal from a first specific pixelof a solid state image pickup device; calculating an output signal froma second specific pixel of the solid state image pickup device;generating a control signal by a predetermined arithmetic operationusing the output signal from the first specific pixel and the outputsignal from the second specific pixel of the solid state image pickupdevice; and performing a predetermined correction process to a luminancesignal by using the control signal.

[0019] Further, from the third aspect of the present invention, there isprovided a video signal processing device for processing a luminancesignal of a video signal generated by causing a solid state image pickupdevice to receive light transmitted through color filters, comprising:first signal operation means for calculating an output signal from aspecific pixel of the solid state image pickup device; second signaloperation means for calculating an average of output signals from allpixels of the solid state image pickup device; control signal generationmeans for generating a control signal by a predetermined arithmeticoperation using the output signal from the specific pixel and theaverage of the output signals from all the pixels of the solid stateimage pickup device; and correction means for performing a predeterminedcorrection process to the luminance signal by using the control signal.

[0020] Further, from the fourth aspect of the present invention, thereis provided a video signal processing device for processing a luminancesignal of a video signal generated by causing a solid state image pickupdevice to receive light transmitted through color filters, comprising:first signal operation means for calculating an output signal from afirst specific pixel of a solid state image pickup device; second signaloperation means for calculating an output signal from a second specificpixel of the solid state image pickup device; control signal generationmeans for generating a control signal by a predetermined arithmeticoperation using the output signal from the first specific pixel and theoutput signal from the second specific pixel of the solid state imagepickup device; and correction means for performing a predeterminedcorrection process to a luminance signal by using the control signal.

[0021] In the video signal processing method and the video signalprocessing device, the predetermined arithmetic operation is performedby using the output signal from the specific pixel of the solid stateimage pickup device and the output signals (or output signal fromanother specific pixel) of all the pixels, so that the control signalhaving a value corresponding to a characteristic difference of colorfilters is generated. Therefore, when a correction process is performedto a video signal by using the control signal, the characteristicdifference of the color filters can be suppressed. As a result, flickerscan be suppressed from being generated.

[0022] Further, from the fifth aspect of the present invention, there isprovided a luminance signal processing circuit for a color video camera,generating a luminance signal from an output signal from a solid stateimage pickup device having a plurality of lines obtained by repeating apair of pixels having color filters, the luminance signal processingcircuit comprising: a circuit in which a light transmittance of one ofthe pair of pixels and a light transmittance of the other arerepresented by T1 and T2, respectively, a photo detection signal fromone of the pair of pixels is multiplied by (T1+T2)/(2×T1) in advance, aphoto detection signal from the other of the pair of pixels ismultiplied by (T1+T2)/(2×T2), and the luminance signal is generated by alow-frequency component of a signal obtained by synthesizing these photodetection signals.

[0023] Preferably, the solid state image pickup device may be a CCDsolid state image pickup device. A combination of the color filters ofthe pair of pixels may be a combination having a small variation incolor temperature. In addition, the combination of the color filters maybe a combination of a filter having. a transparent spectrum or an almosttransparent spectrum and a green filter. Furthermore, the combination ofthe color filters may be a combination of a magenta filter and a greenfilter.

[0024] Furthermore, from the sixth aspect of the present invention,there is provided a luminance signal processing circuit for a colorvideo camera, generating a luminance signal from an output signal from asolid state image pickup device having a plurality of lines obtained byrepeating a pair of pixels having color filters, the luminance signalprocessing circuit comprising: a circuit in which an output signal fromone of the pair of pixels and an output signal from the other arerepresented by T1 and T2, respectively, low-frequency components of theoutput signals T1 and T2 are represented by T1L and T2L, respectively,and conversions expressed by the following equations:

T 1′=T 1×(T 1 L+T 2 L)/(2×T 2 L)

T 2′=T 2×(T 1 L+T 2 L)/(2×T 1 L)

[0025] are performed to the pixels of the respective lines to generatethe luminance signal.

[0026] Further, from the seventh aspect of the present invention, thereis provided a luminance signal processing circuit for a color videocamera, generating a luminance signal from an output signal from a solidstate image pickup device having a plurality of lines obtained byrepeating a pair of pixels having color filters, the luminance signalprocessing circuit comprising: a circuit in which an output signal fromone of the pair of pixels and an output signal from the other arerepresented by T1 and T2, respectively, low-frequency components of theoutput signals T1 and T2 are represented by T1L and T2L, respectively,and conversions expressed by the following equations:

T 1′=2×T 1×T 2 L/(T 1 L+T 2 L)

T 2′=2×T 2×T 1 L/(T 1 L+T 2 L)

[0027] are performed to the pixels of the respective lines to generatethe luminance signal.

[0028] Preferably, the solid state image pickup device may be a CCDsolid state image pickup device. The combination of the. color filtersmay be a combination of a filter having a transparent spectrum or analmost transparent spectrum and a green filter. In addition, thecombination of the color filters may be a combination of a magentafilter and a green filter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0029]FIG. 1 is a view showing an example of the arrangement of acomplementary color filter of a CCD solid state image pickup device of acolor video camera.

[0030]FIG. 2 is a graph used for explaining the cause of generation offlickers.

[0031]FIG. 3 is a view showing an example of color filters of a CCDsolid state image pickup device of a color video camera.

[0032]FIG. 4 is a block diagram showing the arrangement of a main partof a video camera according to the first embodiment to which a videosignal processing method and a video signal processing device accordingto the present invention are applied.

[0033]FIG. 5 is a graph for explaining the relationship between thetransmittances and wavelengths of complementary signals and luminancesignals obtained by a complementary filter.

[0034]FIG. 6 is a graph showing used for explaining a luminancedifference.

[0035]FIG. 7 is a graph used for explaining complementary color signalsand a control signal for controlling a correction amount of a coringprocess.

[0036]FIG. 8 is a graph showing the relationship between inclinationsbased on a coring coefficient and a coring point in the coring process.

[0037]FIG. 9 is a table showing the correspondence between a controlsignal, a coring range, and a coring coefficient.

[0038]FIG. 10 is a block diagram of a system using a luminance signalprocessing circuit for a color video camera according to the secondembodiment of the present invention.

[0039]FIG. 11 is a view for explaining a transfer of charges in a CCDsolid state image pickup device of a color video camera having aluminance signal processing circuit for a color video camera accordingto the second and third embodiments of the present invention.

[0040]FIG. 12 is a view showing another example of a color filter arrayused in the CCD solid state image pickup device of the color videocamera according to the second and third embodiments of the presentinvention.

[0041]FIG. 13 is a block diagram of a system using a luminance signalprocessing circuit for the color video camera according to the thirdembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0042] Preferred embodiments of a video signal processing method and avideo signal processing device according to the present invention willbe described below with reference to the accompanying drawings.

[0043] (First Embodiment)

[0044] A video signal processing method and a video signal processingdevice according to the first embodiment of the present invention can beapplied to a video camera in which a video signal picked up by, e.g., asolid state image pickup device (charge coupled device: CCD) is recordedon a tape-like recording medium such as a magnetic tape, a disk-likerecording medium such as a magnetic disk or an optical disk, or asemiconductor memory or a removable semiconductor memory card arrangedin the device.

[0045] A solid state image pickup device used in a video cameraaccording to this embodiment employs a solid state image pickup deviceusing a so-called all-pixel reading system which independently readssignal charges of all the pixels in a field period and outputs thesignal charges without mixing them so that high horizontal and verticalresolutions of an object can be obtained, even if the object is quicklymoving. In addition, in this embodiment, in order to reduce the size ofthe device arrangement and costs, this solid state image pickup deviceis of a single-plate type. In order to realize a sensitivity higher thanthat of a primary color filter, on the light-receiving surface of thesolid state image pickup device, W (white), G (green), Cy (cyan), and Ye(yellow) complementary color filters having different spectralcharacteristics are arranged in correspondence with pixels.

[0046] The arrangement of a main part of a video camera according to thefirst embodiment of the present invention is shown in FIG. 4. Referringto FIG. 4, for a simple illustration, a lens optical system, a recordingsystem for a recording medium, various signal processing systems, anoperation system, and the like which are generally provided in a videocamera will be omitted.

[0047] In FIG. 4, light which is emitted from an object or the likecomes through a lens optical system (not shown) and complementary colorfilters to form an image on a solid state image pickup device (to bereferred to as a CCD 1 hereinafter). In the CCD 1, the incident light issubjected to photoelectric conversion, and an obtained imaging signal issupplied to a correlated double sampling circuit (CDS) 2.

[0048] This correlated double sampling circuit 2 is a circuit forperforming a so-called correlated double sampling process which is anoise reduction method of removing random noise (shot noise of a signaland a dark current) of the CCD 1. More specifically, a process ofsuppressing reset noise by subtracting the level of a field throughperiod from a signal period level. An output from the correlated doublesampling circuit 2 is supplied to an analog/digital (A/D) converter 3.

[0049] The analog/digital converter 3 includes a sample holding circuiton the input side and samples an analog imaging signal sample-held bythe sample holding circuit at a predetermined sampling frequency toconvert the analog imaging signal into a digital signal (to be referredto as a digital video signal hereinafter). The digital video signaloutput from the analog/digital converter 3 is supplied to a verticalfilter circuit 4, a main signal processing circuit 6, and a pixelseparation circuit 8.

[0050] The vertical filter circuit 4 has, at least, a vertical band-passfilter (V-BPF) for extracting a predetermined frequency band componentin the vertical direction from the digital video signal and a verticalhigh-pass band filter (V-HPF) for extracting a high-frequency bandcomponent in the vertical direction from the digital video signal. Thevertical filter circuit 4 extracts a frame component in the verticaldirection from the digital video signal. The vertical band-pass filterand the vertical high-pass filter are infinite impulse response (IIR)digital filters or finite impulse response (FIR) digital filters. Forexample, a five-tap filter coefficient is set for the vertical high-passfilter, and a three-tap filter coefficient is set for the verticalband-pass filter. An output signal from the vertical filter circuit 4,i.e., a contour component in the vertical direction extracted from thedigital video signal is supplied to a coring process circuit 5.

[0051] The coring process circuit 5 performs a so-called coring processwhich suppresses a noise component included in the contour component ofan image to improve a signal/noise ratio (S/N). At the same time, in thecoring process circuit 5, due to the characteristic difference betweencomplementary color filters of W, G, Cy, and Ye as shown in FIG. 1, aspectral difference (luminance difference) generated between a luminancesignal (Ya=W+G) consisting of W and G and a luminance signal (Yb=Cy+Ye)consisting of Cy and Ye is suppressed by controlling a coring correctionamount in the coring process. As a result, a correction process forsuppressing flickers is also performed.

[0052] The correction process for suppressing flickers in the coringprocess circuit 5 will be described below.

[0053] In the complementary color filters of W, G, Cy, and Ye shown inFIG. 1, the respective color filters have the relationship between alight transmittance and a waveform as shown in FIG. 5. It is understoodfrom FIG. 5 that the color filter has a high transmittance on ashort-wavelength side. It is also understood from FIG. 5 that aluminance Y (Ya, Yb) is spectrum having a wavelength centered at about550 nm. Here, when the following equations are satisfied:

Ya=W+G

Yb=Cy+Ye,

[0054] it is understood that Ys (luminance difference)=(Ya−Yb)/Ya islarge on the short-wavelength side as shown in FIG. 6.

[0055] Therefore, the following may be understood. That is, when acontrol signal having a correction value (coring correction value) whichincreases on the short-wavelength side with respect to a luminancesignal is supplied to the coring process circuit 5, flickers can besuppressed. As shown in FIG. 5, a color signal of Cy having a hightransmittance on the short-wavelength side may be used. However, whenthe color signal of Cy is directly used as a control signal for thecorrection amount in the coring process circuit 5, the control signal isnot appropriate because the control signal has the maximum correctionamount obtained at a wavelength of about 500 nm.

[0056] In contrast to this, it is understood that a signal obtained bycalculating, e.g., Cy/Y is a signal having a value which increases asthe wavelength decreases as shown in FIG. 7. Therefore, according tothis embodiment, the signal obtained by calculating Cy/Y is supplied tothe coring process circuit 5 as a control signal yf1 having a correctionvalue which increases on the short-wavelength side with respect to theluminance signal. In this embodiment, the control signal yf1 isgenerated by a moire process circuit 9 (to be described later) to besupplied to the coring process circuit 5. In FIG. 7, for comparison withthe control signal yf1 obtained by calculating Cy/Y, the characteristicsof complementary color signals of W, Ye, Cy, and G are also shown.

[0057] More specifically, in the coring process circuit 5, the controlsignal yf1 obtained by calculating Cy/Y and supplied from the moireprocess circuit 9 is classified by five stages (vck1, vck2, vck3, andvck4) according to the transmittance as shown in FIG. 7. On thelong-wavelength side, a correction amount (coring correction amount) inthe coring process circuit 5 is decreased; and on the short-wavelengthside, a correction amount (coring correction amount) in the coringprocess circuit 5 is increased. As a result, the coring correctionamount is increased for a video signal from an object including a largeamount of short-wavelength component having a large luminance difference(Ys=(Ya−Yb)/Ya) shown in FIG. 6, and the luminance difference can becompressed. On the other hand, the coring correction amount decreases onthe long-wavelength side (or correction is not performed), so that imagequality can be prevented from being degraded.

[0058] In the coring process circuit 5, in order to realize correctionamount control (control of a coring correction amount) for the luminancesignal, a microcomputer sets inclinations k=1, k=12/16, k=8/16, k=6/16,k=4/16, k=0, and the like based on a coring coefficient kys as shown inFIG. 8, coring points yh1c and −yh1c, and a corresponding table or thelike between a coring range shown in FIG. 9 and the coring coefficientkys, so that coring coefficients (inclinations, i.e., coring correctionamounts) are selectively switched by the control signal yf1 to be set.The range subjected to coring is set as a coring point by themicrocomputer.

[0059] In this embodiment, the coring range can be switched depending onan arithmetic operation method (a=0, b=1) of a moire process in themoire process circuit 9 (to be described later). For example, as shownin FIG. 9, a coring range used when the moire process is a (=0,a→y+1=CyL/YL) is given such that the coring coefficient kys=16 whenvck1≦yf1 is satisfied; the coring coefficient kys=12 when vck2≦yf1<vck1is satisfied; the coring coefficient kys=10 when vck3≦yf1<vck2 issatisfied; the coring coefficient kys=8 when vck4≦yf1<vck3 is satisfied;and the coring coefficient kys=4 when 0≦yf1<vck4. On the other hand, acoring range used when the moire process is b(=0, b→y+1=YL/CyL) is givensuch that the coring coefficient kys=4 when vck1≦yf1 is satisfied; thecoring coefficient kys=8 when vck2≦yf1<vck1 is satisfied; the coringcoefficient kys=10 when vck3£yf1<vck2 is satisfied; the coringcoefficient kys=12 when vck4≦yf1<vck3 is satisfied; and the coringcoefficient kys=16 when 0≦yf1<vck4. As a matter of course, independentlyof the method of the moire process, the coring correction amount may becontrolled.

[0060] In this embodiment, although the signal obtained by calculatingCy/Y is defined as the control signal yf1, a signal obtained bycalculating Cy/Y1 (Y1 is the low-frequency component of a Y signal) isalso defined as the control signal yf1, and a signal obtained bycalculating Cy1/Y1 (Cy1 is the low-frequency component of a Cy signal)is also defined as the control signal yf1. Similarly, a signal generatedby using an operation expression such as Cy1/Ye1 (Ye1 is thelow-frequency component of a Ye signal) or Y1/Ye1 can also be defined asthe control signal yf1. When the operation expression such as Cy1/Ye1 orY1/Ye1 is used, a correction amount on the short-wavelength side can becontrolled. When the inverse of the operation expression is used, acorrection amount on the long-wavelength side can also be controlled.

[0061] Returning to FIG. 4, a signal subjected to the coring process bythe coring process circuit 5 is supplied to a pre-γ (gamma) contourcompensation circuit 12 and a post-γ contour compensation circuit 14 (tobe described later).

[0062] The main signal processing circuit 6 multiplies predeterminedpixel coefficients kw and kg by W and G in the complementary signals ofW (white), G (green), Cy (cyan), and Ye (yellow) to suppress moirecaused by WG. A timing at which the pixel coefficients kw and kg by Wand G is designed to be switched depending on the array of the colorfilters. A digital video signal (to be referred to as a main signalhereinafter) output from the main signal processing circuit 6 issupplied to a vertical low-pass filter (V-LPF) 7.

[0063] Since the vertical low-pass filter 7 adds a contour component,i.e., a high-frequency component, to a main signal in the pre-γ contourcompensation circuit 12 of the post stage, high-frequency components inthe horizontal and vertical directions are removed from the main signalas the previous process. The vertical low-pass filter 7 is afinite orinfinite impulse response digital filter. For example, a five-tap filtercoefficient is set for the vertical low-pass filter 7. The main signalfrom which the high-frequency component is removed by the verticallow-pass filter 7 is supplied to the pre-γ contour compensation circuit12.

[0064] Since digital video signals supplied from the analog/digitalconverter 3 are signals which are sequentially supplied according to thearray of complementary color filters of W, G, Cy, and Ye, the pixelseparation circuit 8 separates the sequentially supplied signals fromsignals from pixels corresponding to W, G, Cy, and Ye. In the pixelseparation circuit 8, in order to interpolate portions correspondingpixels removed by the pixel separation (to arrange complementary colorsignals at portions corresponding to the removed pixels), pixelinterpolation in, e.g., the horizontal direction may also be performed.The signals output from the pixel separation circuit 8 are supplied tothe moire process circuit 9.

[0065] The moire process circuit 9 balances the levels of thecomplementary color signals of W, G, Cy, and Ye supplied from the pixelseparation circuit 8 to perform a moire process for suppressing moire.An output signal from the moire process circuit 9 is supplied to ahorizontal high-pass filter (H-HPF) 10. The above-described controlsignal yf1 used in the coring process circuit 5 is also output from themoire process circuit 9.

[0066] In the horizontal high-pass filter 10, a high-frequency bandcomponent is extracted from a supplied signal. More specifically, ahorizontal high-frequency component subjected to a moire process isoutput from the horizontal high-pass filter 10. An output signal fromthe horizontal high-pass filter 10 is supplied to a coring processcircuit 11.

[0067] The coring process circuit 11 has almost the same arrangement asthat of the coring process circuit 5. The coring process circuit 11suppresses a noise component included in the high-frequency component ofthe signal supplied from the horizontal high-pass filter 10 to perform acoring process for improving a signal/noise (S/N) ratio. The horizontalhigh-frequency component subjected to the moire process and subjected tothe coring process by the coring process circuit 11 is supplied to thepre-γ contour compensation circuit 12.

[0068] The pre-γ contour compensation circuit 12 mixes a horizontalcontour component obtained by the vertical filter circuit 4 and thecoring process circuit 5, the main signal which is obtained by the mainsignal processing circuit 6 and the vertical low-pass filter 7 and fromwhich a high-frequency component is removed, and the horizontalhigh-frequency component which is obtained by the arrangement extendingfrom the pixel separation circuit 8 to the coring process circuit 11 andwhich is subjected to the moire process and the coring process to eachother to constitute a luminance signal and to compensate for the contourof the luminance signal. A video signal subjected to contourcompensation by the pre-γ contour compensation circuit 12 is supplied toa gamma process circuit 13.

[0069] The gamma process circuit 13 performs a γ-(gamma-) correctionprocess, for correcting the gamma characteristics of a CRT (cathode raytube) to be used as a display device, to a digital video signal suppliedfrom the pre-γ contour compensation circuit 12. The video signalsubjected to the gamma correction process by the gamma process circuit13 is supplied to a post-γ contour compensation circuit 14 and ahorizontal aperture-control circuit 16.

[0070] In the horizontal aperture-control circuit 16 performs ahorizontal (or vertical) aperture correction to the video signalsubjected to the gamma correction process by the gamma process circuit13 to the video signal subjected to the aperture correction to a coringprocess circuit 15.

[0071] The coring process circuit 15 also has almost the samearrangement as that of the coring process circuit 11 or the coringprocess circuit 5 and suppresses noise component included in thehigh-frequency band component of the video signal to perform a coringprocess for improving a signal/noise (S/N) ratio. An output signal fromthe coring process circuit 15 is supplied to the post-γ contourcompensation circuit 14.

[0072] The post-γ contour compensation circuit 14 mixes a verticalcontour component obtained by the vertical filter circuit 4 and thecoring process circuit 5, a video signal subjected to the gammacorrection process and output from the gamma process circuit 13, and thesignal subjected to horizontal aperture correction to each other tocompensate for the contour of a luminance signal subjected to the gammacorrection process.

[0073] An output signal from the post-γ contour compensation circuit 14is output as a digital video signal of the video camera of thisembodiment or recorded on a recording medium.

[0074] As described above, in the video camera of this embodiment, themoire process circuit 9 generates the control signal yf1 by calculating,e.g., Cy/Y, and the coring process circuit 5 control a coring correctionamount on the basis of the control signal yf1. More specifically, thecoring process circuit 5 performs the coring process such that acorrection amount of the coring process is decreased (or the coringprocess is not performed) on the long-wavelength side and is increasedon the short-wavelength side. A luminance difference is compressed withrespect to a video signal from an object including a large amount ofshort-wavelength component having a large luminance difference. On theother hand, image quality can be prevented from being degraded on thelong-wavelength side. As a result, in the video camera of thisembodiment, flickers caused by the characteristic difference betweencomplementary color filters can be suppressed.

[0075] In the vertical filter circuit 4 having the arrangement shown inFIG. 4, the filter coefficients of the vertical band-pass filter and thevertical high-pass filter are set at predetermined values. However, thefilter coefficient of the vertical band-pass filter may be set at apredetermined value, and the rate of the vertical high-pass filter maybe switched. A switch used at this time may be designed to be controlledby an external circuit.

[0076] Immediately after the coring process circuit 5, a switchingcircuit which mixes signals of two lines through a line memory if anoutput signal from the coring process circuit 5 is saturated or directlyoutputs the signals if the output signal is not saturated may also bearranged. In this case, saturation data from the CCD 1 is supplied tothe switching circuit, and a gain coefficient for gain control set bythe microcomputer is input to the switching circuit. If it is detectedfrom the saturation data that the output signal from the coring processcircuit 5 is saturated, signals of two lines are mixed to each otherthrough, e.g., a line memory. If the output signal is not saturated, aswitching output is performed to directly output the signals, and theswitching output is multiplied by the gain coefficient. Control of theswitching output in the switching circuit can also be performed by aswitching change-over signal, and a mixture signal of the two linesobtained through the line memory can also be always output. When theswitching circuit is arranged, the output signal from the switchingcircuit is supplied to the pre-γ contour compensation circuit 12 and thepost-γ contour compensation circuit 14.

[0077] In addition, in order to improve a signal/noise (S/N) ratio,horizontal low-pass filters can also be arranged between the verticalfilter circuit 4 and the coring process circuit 5 and between thevertical low-pass filter 7 and the pre-γ contour compensation circuit12, respectively.

[0078] In the gamma process circuit 13, the above process and the a kneeprocess can also be performed at the same time.

[0079] (Second Embodiment)

[0080] The second embodiment of the present invention will be describedbelow with reference to FIGS. 10 to 12. FIG. 10 is a view showing thearrangement of the outline of the embodiment in which the presentinvention is applied to a color video camera. The same referencenumerals as in FIG. 4 denote the same parts in FIG. 10, and anoverlapping description will be omitted.

[0081] In this embodiment, as will be described later, a digital signal(to be referred to as a main signal hereinafter) from which a falsesignal is removed by a main signal processing circuit 6 is sequentiallysupplied to a vertical low-pass filter (V-LPF) 7 a and a horizontallow-pass filter (H-LPF) 7 b.

[0082] Since the vertical low-pass filter (V-LPF) 7 a and the horizontallow-pass filter (H-LPF) 7 b add a contour component, i.e., ahigh-frequency component to a main signal in a pre-γ contourcompensation circuit 12 of the post stage, a high-frequency component isremoved from the main signal as the previous process. The verticallow-pass filter 7 a is a finite or infinite impulse response digitalfilter. For example, a five-tap filter coefficient is set for thevertical low-pass filter 7 a. The main signal from which thehigh-frequency component is removed by the vertical low-pass filter 7 aand the horizontal low-pass filter 7 b is supplied to the pre-γ contourcompensation circuit 12.

[0083] The pre-γ contour compensation circuit 12 mixes a verticalcontour component obtained by a vertical filter circuit 4 and a coringprocess circuit 5, the main signal which is obtained by a main signalprocessing circuit 6 and the vertical low-pass filter 7 a and thehorizontal low-pass filter 7 b and from which a high-frequency componentis removed, and the horizontal high-frequency component which isobtained by the arrangement extending from a pixel separation circuit 8to a coring process circuit 11 and which is subjected to a moire processand a coring process to each other to constitute a luminance signal andto compensate for the contour of the luminance signal. A video signalsubjected to contour compensation by the pre-γ contour compensationcircuit 12 is supplied to a gamma process circuit 13.

[0084] The process in the main signal processing circuit 6 serving as amain part of this embodiment will be described below.

[0085] As the color filter array of a CCD 1 used in this camera, a colorfilter array having four pixels of W, G, Cy, and Ye as one unit isused,as shown in FIG. 3. In FIG. 3, reference symbol Px denotes a pixel pitchin the horizontal direction, and reference symbol Py denotes a pixelpitch in the vertical direction.

[0086] In the CCD 1, as shown in FIG. 11, charges of all pixelsaccumulated in a photoelectric conversion element 18 are transferred toa vertical CCD 19 to be read by a horizontal CCD 20 in units of lines.An interleave system which reads signals every other line, a systemwhich uses two horizontal CCDs, and the like are known. If any system isused, the same process as described above can be performed.

[0087] Therefore, a signal having a series of W, G, W, G, . . . and asignal having a series of Cy, Ye, Cy, Ye, . . . can be obtained. In thisembodiment, a conversion process is performed to the signal having theWG series.

[0088] With respect to the horizontal direction, a luminance resolutioncorresponding a spatial frequency of 1/Px can be generally expected.However, when a signal S having the WG series passes through a low-passfilter, the signal S includes a false signal due to the differencebetween a W signal and a G signal in intensity. When a carrier frequencyis represented by fs, the signal S is given by:

S=(W+G)/2+(π/2)×(W−G) sin(2π×fs×t)  (1)

[0089] Here, the first term is an original luminance signal, and thesecond term is a false signal. On the other hand, the difference betweenthe W signal and the G signal in intensity is largely dependent on adifference between color filters in light transmittance. Therefore,conversions given by the following equations are performed:

Kw=(Tw+Tg)/2Tw

Kg=(Tw+Tg)/2Tg

W′=Kw×W

G′=Kg×G

[0090] The conversions are performed such that a digital video signalsupplied from the analog/digital converter 3 is multiplied bypredetermined constants Kw and Kg, and are performed by a multiplierarranged in the main signal processing circuit 6.

[0091] Here, reference symbol Tw denotes the light transmittance of a Wpixel, and Tg denotes the light transmittance of a G pixel. In thiscase, since the W pixel basically transmits all incident light, no colorfilter does not substantially exist. More specifically, the color filterof the W pixel has a transparent spectrum or an almost transparentspectrum.

[0092] However, for descriptive convenience, the light transmittance ofthe color filter of the W pixel is defined as a light transmittanceequal to that of a general color filter. More specifically, the lighttransmittance of the W pixel is generally considered as 1. In this case,when flat white light is incident on the W pixel, the followingrelationships are satisfied:

W′+G′=Kw×W+Kg×G

Kw×W′=Kg×G′

[0093] In this manner, W and G are converted into W′ and G′,respectively. When W′ and G′ are substituted in Equation (1), a signalS′ being free from a false signal is obtained in the following manner:$\begin{matrix}{{S^{\prime} = {{( {W^{\prime} + G^{\prime}} )/2} + {( {\pi/2} ) \times ( {W^{\prime} - G^{\prime}} )\sin \quad ( {2\quad \pi \times f\quad s \times t} )}}}\quad} \\{= {( {W + G} )/2}}\end{matrix}$

[0094] In general, since (W′−G′) is compressed more greatly than (W−G),it is understood that the false signal is reduced.

[0095] In this manner, the low-pass filters 7 a and 7 b removes apredetermined high-band component from a signal whose false signal isreduced in the main signal processing circuit 6 to generate a luminancesignal.

[0096] Even in a filter other than the W and G filters, when the filteris slightly influenced by a color temperature like the W and G filters,the filter rarely depends on the spectrum of incident light. For thisreason, the above conversions are effective. For example, even in a CCDsolid state image pickup device having a color array including fourpixels of Mg (magenta), G (green), Cy (cyan), and Ye (yellow) as oneunit, the same process as described above is effective. In this case,conversion processes are given by the following equations:$\begin{matrix}{{Km} = {{( {{Tm} + {Tg}} )/2}{Tm}}} \\{{Kg} = {{( {{Tm} + {Tg}} )/2}{Tg}}} \\{{Mg}^{\prime} = {{Km} \times {Mg}}} \\{G^{\prime} = {{Kg} \times G}}\end{matrix}$

[0097] Here, reference symbol Tm denotes the light transmittance of theMg pixel, and Tg denotes the light transmittance of the G pixel.

[0098] (Third Embodiment)

[0099] The third embodiment of the present invention will be describedbelow with reference to FIGS. 11 to 13. FIG. 13 is a view showing thearrangement of the outline of the third embodiment in which the presentinvention is applied to a color video camera. The same referencenumerals as in FIGS. 4 and 10 denote the same parts in FIG. 13, and anoverlapping description will be omitted.

[0100] In this embodiment, a signal output from a pixel separationcircuit 8 and a signal from which a high-frequency component is removedthrough a horizontal low-pass filter (H-LPF) 8 a is supplied to a moireprocess circuit 9.

[0101] A process for digital video signals sequentially supplied fromthe pixel separation circuit 8 will be described below in detail.

[0102] In Equation (1) described above, the first term is an originalluminance signal, and the second term is a false signal generated by afolding component. Conversions given by the following equations areperformed to respective pixels of input lines: $\begin{matrix}{W^{\prime} = {2 \times W \times {{GL}/( {{WL} + {GL}} )}}} \\{G^{\prime} = {2 \times G \times {{WL}/( {{WL} + {GL}} )}}} \\{{Cy}^{\prime} = {2 \times {Cy} \times {{YeL}/( {{CyL} + {YeL}} )}}} \\{{Ye}^{\prime} = {2 \times {Ye} \times {{CyL}/( {{CyL} + {YeL}} )}}}\end{matrix}$

[0103] Here, WL, GL, CyL, and YeL are the low-frequency components ofoutput signals W, G, Cy, and Ye from the CCD, respectively. Morespecifically, the low-frequency components are calculated from severalpixels after and before a target pixel, e.g., 5 to 15 pixels, throughthe horizontal low-pass filter 8 a. The conversions are performed insidethe moire process circuit 9.

[0104] When these conversions are performed, a low-frequency-regioncomponent SwL and a high-frequency-region component SwH of W of a signalof a WG line calculated from W′, G′, Cy′, and Ye′ obtained afterconversion are given by the following equations:

SwL=2×W×GL/(WL+GL)

SwH=2×W×GL/(WL−GL)

[0105] On the other hand, a low-frequency-region component SgL and ahigh-frequency-region component SgH of W of the signal of the WG lineare given by the following equations:

SgL=2×G×WL/(WL+GL)

SgH=−2×G×WL/(WL−GL)

[0106] Similarly, a low-frequency-region component ScyL and ahigh-frequency-region component ScyH of Cy of a signal of a CyYe lineare given by the following equations:

ScL=2×Cy×YeL/(CyL+YeL)

ScH=2×Cy×YeL/(CyL−YeL)

[0107] In addition, a low-frequency-region component ScyL and ahigh-frequency-region component ScyH of Ye of the signal of the CyYeline are given by the following equations:

ScL=2×Ye×CyL/(CyL+YeL)

SyH=−2×Ye×CyL/(CyL−YeL)

[0108] Therefore, it is understood that folding components in thehigh-frequency regions have equal levels in the pixels. In a prior art,the luminance component is averaged by a low-pass filter. However,according to the present invention, the above operation is performedwithout performing addition in the horizontal direction.

[0109] Since the effect of a spectrum by the above operation isequivalent to the effect of a common spectrum component of each pixel,i.e., a G spectrum, the operation result is a process in a frequencyband (luminance band) which does not influence color reproduction.

[0110] The above effect can also be obtained by using the followingconversions: $\begin{matrix}{W^{\prime} = {W \times {( {{WL} + {GL}} )/( {2 \times {WL}} )}}} \\{G = {G \times {( {{WL} + {GL}} )/( {2 \times {GL}} )}}} \\{{Cy}^{\prime} = {{Cy} \times {( {{CyL} + {YeL}} )/( {2 \times {CyL}} )}}} \\{{Ye}^{\prime} = {{Ye} \times {( {{CyL} + {YeL}} )/( {2 \times {YeL}} )}}}\end{matrix}$

[0111] The same conversions as described above may be performed in thevertical direction. More specifically, the presence of a difference inthe vertical direction is equivalent to the presence of a difference inthe horizontal direction. The luminance of the WG line and the luminanceof the CyYe line are represented by Yw and Yc, respectively, andconversions expressed by the following equations may be performed:

Yw′=Yw/(YwL+YcL)

Yc′=Yc/(Ywl+YcL)

[0112] Here, a letter L is also added to represent alow-frequency-region component.

[0113] The CCD solid state image pickup device having a color arrayincluding four pixels of W, G, Cy, and Ye as one unit has been describedabove. However, the present invention is not limited to this embodiment,and the above conversions are effective for a filter of another type.For example, even if a CCD solid state image pickup device having acolor array including four pixels of Mg (magenta), G, Cy, and Ye, asshown in FIG. 12, as one unit, the same process as described above iseffective. In this case, as a conversion process, conversions expressedby the following equations are performed:Input  Workspace  TL4Date:08/14/2003  Number:10386461  Folder:03

[0114] The present invention is not limited to the above embodiments,and various changes can be effected according to design or the likewithout departing from the spirit and scope of the present invention.The present invention can also be applied to an image pickup apparatusother than a video camera, e.g., a digital still camera. The readingsystem of the CCD can be applied to not only the all-pixel readingsystem but also other various reading systems. In the first embodiment,complementary color filters of W, G, Cy, and Ye are arranged on the CCD.However, the present invention can also be applied to a case whereincomplementary color filters of Mg (magenta), G, Cy, and Ye are used.

[0115] In the arrangement of each of the above embodiments, a part forperforming digital signal processing is expressed as a circuitarrangement. However, operations performed by these circuits can also beexecuted by software by means of a digital signal processors (DSP) orthe like, as a matter of course. If the arrangement in which digitalsignal processing is realized by software is used, various set valuesand operations can be changed by changing the software, as a matter ofcourse.

What is claimed is:
 1. A video signal processing method of processing aluminance signal of a video signal generated by causing a solid stateimage pickup device to receive light transmitted through color filters,comprising the steps of: calculating an output signal from a specificpixel of the solid state image pickup device; calculating an average ofoutput signals from all pixels of the solid state image pickup device;generating a control signal by a predetermined arithmetic operationusing the output signal from the specific pixel and the average of theoutput signals from all the pixels of the solid state image pickupdevice; and performing a predetermined correction process to theluminance signal by using the control signal.
 2. A video signalprocessing method according to claim 1, wherein, in the step ofcalculating an output signal from a specific pixel of the solid stateimage pickup device, a low-frequency component of the output signal fromthe specific pixel is calculated.
 3. A video signal processing methodaccording to claim 1, wherein, in the step of calculating an average ofoutput signals from all pixels of the solid state image pickup device,an average of low-frequency components of the output signals from allthe pixels.
 4. A video signal processing method according to claim 1,wherein, in the step of generating a control signal, the output signalfrom the specific pixel is divided by the output signals from all thepixels to generate the control signal.
 5. A video signal processingmethod according to claim 1, further comprising the step of classifyingthe control signal in a plurality of stages; wherein, in the step ofperforming a predetermined correction process to the luminance signal byusing the control signal, the predetermined correction process isperformed to the luminance signal depending on the classified controlsignals of the respective stages.
 6. A video signal processing methodaccording to claim 1, wherein, in the step of generating a controlsignal, the output signals from all the pixels are divided by the outputsignal from the specific pixel to generate a control signal.
 7. A videosignal processing method according to claim 5, wherein, in the step ofperforming a predetermined correction process to the luminance signal byusing the control signal, the predetermined correction process isperformed to a short-wavelength side of the luminance signal by thecontrol signal, and the predetermined correction process is performed toa long-wavelength side of the luminance signal by an inverse of thecontrol signal.
 8. A video signal processing method of processing aluminance signal of a video signal generated by causing a solid stateimage pickup device to receive light transmitted through color filters,comprising the steps of calculating an output signal from a firstspecific pixel of the solid state image pickup device; calculating anoutput signal from a second specific pixel of the solid state imagepickup device; generating a control signal by a predetermined arithmeticoperation using the output signal from the first specific pixel and theoutput signal from the second specific pixel of the solid state imagepickup device; and performing a predetermined correction process to theluminance signal by using the control signal.
 9. A video signalprocessing method according to claim 8, wherein, in the steps ofcalculating output signals from first and second specific pixels of thesolid state image pickup device, low-frequency components of the outputsignals from the first and second specific pixels are calculated.
 10. Avideo signal processing method according to claim 8, wherein, in thestep of generating a control signal, the output signal from the firstspecific pixel is divided by the output signal from the second specificpixel to generate the control signal.
 11. A video signal processingmethod according to claim 8, wherein, in the step of performing apredetermined correction process to the luminance signal by using thecontrol signal, the predetermined correction process is performed to ashort-wavelength side of the luminance signal by the control signal, andthe predetermined correction process is performed to a long-wavelengthside of the luminance signal by an inverse of the control signal.
 12. Avideo signal processing device for processing a luminance signal of avideo signal generated by causing a solid state image pickup device toreceive light transmitted through color filters, comprising: firstsignal operation means for calculating an output signal from a specificpixel of the solid state image pickup device; second signal operationmeans for calculating an average of output signals from all pixels ofthe solid state image pickup device; control signal generation means forgenerating a control signal by a predetermined arithmetic operationusing the output signal from the specific pixel and the average of theoutput signals from all the pixels of the solid state image pickupdevice; and correction means for performing a predetermined correctionprocess to the luminance signal by using the control signal.
 13. A videosignal processing device according to claim 12, wherein the first signaloperation means has low-frequency component extracting means forextracting a low-frequency component of the output from the specificpixel.
 14. A video signal processing device according to claim 12,wherein the second signal operation means has low-frequency componentextracting means for extracting low-frequency components of the outputsignals from all the pixels to calculate an average of the low-frequencycomponents of the output signals from all the pixels.
 15. A video signalprocessing device according to claim 12, wherein the control signalgeneration means has division means for dividing the output signal fromthe specific pixel by the output signals from all the pixels to generatea control signal.
 16. A video signal processing device according toclaim 12, further comprising classification means for classifying thecontrol signal in a plurality of stages; wherein the correction meansperforms the predetermined correction process to the luminance signaldepending on the classified control signals of the respective stages.17. A video signal processing device according to claim 12, wherein thecontrol signal generation means has division means for dividing theoutput signals from all the pixels by the output from the specific pixelto generate a control signal.
 18. A video signal processing deviceaccording to claim 17, wherein the correction means performs thepredetermined correction process to a short-wavelength side of theluminance signal by the control signal and the predetermined correctionprocess to a long-wavelength side of the luminance signal by an inverseof the control signal.
 19. A video signal processing device forprocessing a luminance signal of a video signal generated by causing asolid state image pickup device to receive light transmitted throughcolor filters, comprising: first signal operation means for calculatingan output signal from a first specific pixel of a solid state imagepickup device; second signal operation means for calculating an outputsignal from a second specific pixel of the solid state image pickupdevice; control signal generation means for generating a control signalby a predetermined arithmetic operation using the output signal from thefirst specific pixel and the output signal from the second specificpixel of the solid state image pickup device; and correction means forperforming a predetermined correction process for a luminance signal byusing the control signal.
 20. A video signal processing device accordingto claim 19, wherein the first signal operation means has firstlow-frequency component extraction means for extracting a low-frequencycomponent of the output from the first specific pixel, and the secondsignal operation means has second low-frequency component extractionmeans for extracting a low-frequency component of the output from thesecond specific pixel.
 21. A video signal processing device according toclaim 19, wherein, the control signal generation means divide the outputsignal from the first specific pixel by the output signal from thesecond specific pixel to generate a control signal.
 22. A video signalprocessing device according to claim 19, wherein the correction meansperform the predetermined correction process to a short-wavelength sideof the video signal by the control signal and the predeterminedcorrection process to a long-wavelength side of the video signal by aninverse of the control signal.
 23. A luminance signal processing circuitfor a color video camera, generating a luminance signal from an outputsignal from a solid state image pickup device having a plurality oflines obtained by repeating a pair of pixels having color filters, theluminance signal processing circuit comprising: a circuit in which alight transmittance of one of the pair of pixels and a lighttransmittance of the other are represented by T1 and T2, respectively, aphoto detection signal from one of the pair of pixels is multiplied by(T1+T2)/(2×T1) in advance, a photo detection signal from the other ofthe pair of pixels is multiplied by (T1+T2)/(2×T2), and the luminancesignal is generated by a low-frequency component of a signal obtained bysynthesizing these photo detection signals.
 24. A luminance signalprocessing circuit for a color video camera according to claim 23,wherein the solid state image pickup device comprises a CCD solid stateimage pickup device.
 25. A luminance signal processing circuit for acolor video camera according to claim 23, wherein a combination of thecolor filters of the pair of pixels comprises a combination having asmall variation in color temperature.
 26. A luminance signal processingcircuit for a color video camera according to claim 25, wherein acombination of the color filters comprises a combination of a filterhaving a transparent spectrum or an almost transparent spectrum and agreen filter.
 27. A luminance signal processing circuit for a colorvideo camera according to claim 25, wherein a combination of the colorfilters comprises a combination of a magenta filter and a green filter.28. A luminance signal processing circuit for a color video camera,generating a luminance signal from an output signal from a solid stateimage pickup device having a plurality of lines obtained by repeating apair of pixels having color filters, the luminance signal processingcircuit comprising: a circuit in which an output signal from one of thepair of pixels and an output signal from the other are represented by T1and T2, respectively, low-frequency components of the output signals T1and T2 are represented by T1L and T2L, respectively, and conversionsexpressed by the following equations: T 1′=T 1×(T 1 L+T 2 L)/(2×T 2 L)T2′=T 2×(T 1 L+T 2 L)/(2×T 1 L) are performed to the pixels of therespective lines to generate the luminance signal.
 29. A luminancesignal processing circuit for a color video camera, generating aluminance signal from an output signal from a solid state image pickupdevice having a plurality of lines obtained by repeating a pair ofpixels having color filters, the luminance signal processing circuitcomprising: a circuit in which an output signal from one of the pair ofpixels and an output signal from the other are represented by T1 and T2,respectively, low-frequency components of the output signals T1 and T2are represented by T1L and T2L, respectively, and conversions expressedby the following equations: T 1′=2×T 1 ×T 2 L/(T 1 L+T 2 L)T 2′=2×T 2 ×T1 L/(T 1 L+T 2 L) are performed to the pixels of the respective lines togenerate the luminance signal.
 30. A luminance signal processing circuitfor a color video camera according to claim 28, wherein the solid stateimage pickup device comprises a CCD solid state image pickup device. 31.A luminance signal processing circuit for a color video camera accordingto claim 28, wherein a combination of the color filters comprises acombination of a filter having a transparent spectrum or an almosttransparent spectrum and a green filter.
 32. A luminance signalprocessing circuit for a color video camera according to claim 28,wherein a combination of the color filters comprises a combination of amagenta filter and a green filter.